bph - 1 year ago 222

Python Question

Does

`numpy`

`gcd`

I'm aware of

`fractions.gcd`

`numpy`

`numpy`

I have been unable to uncover anything on google other than this link which seems out of date and I don't know how I would access the

`_gcd`

Naively trying:

`np.gcd`

np.euclid

hasn't worked for me...

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Answer Source

You can write it yourself:

```
def numpy_gcd(a, b):
a, b = np.broadcast_arrays(a, b)
a = a.copy()
b = b.copy()
pos = np.nonzero(b)[0]
while len(pos) > 0:
b2 = b[pos]
a[pos], b[pos] = b2, a[pos] % b2
pos = pos[b[pos]!=0]
return a
```

Here is the code to test the result and speed:

```
In [181]:
n = 2000
a = np.random.randint(100, 1000, n)
b = np.random.randint(1, 100, n)
al = a.tolist()
bl = b.tolist()
cl = zip(al, bl)
from fractions import gcd
g1 = numpy_gcd(a, b)
g2 = [gcd(x, y) for x, y in cl]
print np.all(g1 == g2)
True
In [182]:
%timeit numpy_gcd(a, b)
1000 loops, best of 3: 721 us per loop
In [183]:
%timeit [gcd(x, y) for x, y in cl]
1000 loops, best of 3: 1.64 ms per loop
```

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